1. Field of the Invention
This invention relates to an apparatus for detecting the position of a motor-controlled mechanism and, more particularly, to a position detecting apparatus for detecting and controlling the rotational position of a motor associated with, for example, a power mirror assembly or a power seat assembly of a motor vehicle.
2. Description of the Related Art
Recent motor vehicles have been equipped with motor-controlled mechanisms, such as power mirrors and power seats, which are automatically adjusted to a predetermined position based on information stored in memory. To execute this automatic adjustment, a control apparatus is used which includes a position detector to determine the position of, for example, a seat or a mirror, by determining the rotational position of a motor associated with the motor-controlled mechanism. The rotational position of the motor is then compared with a stored position value, and the motor-controlled mechanism is then adjusted.
One of two prior art apparatus are typically used to adjust the above-mentioned motor-controlled mechanisms. A first prior art apparatus includes a potentiometer attached to the rotating shaft of a motor. The first prior art apparatus detects a change in the angle of rotation of the motor shaft by detecting a change in the resistance of the potentiometer. The first prior art apparatus controls the angle of rotation of the motor by generating a control signal corresponding to the resistance of the potentiometer. A second prior art apparatus includes a rotary encoder attached to the rotating shaft of the motor. The second prior art apparatus counts the number of output pulses generated by the rotary encoder, which in turn indicate the rotational speed of the motor when the motor shaft rotates. The second prior art apparatus then controls the angle of rotation of the motor by generating a control signal corresponding to the detected number of pulses.
FIG. 3 is a schematic diagram of the configuration of an example of the first prior art apparatus, and FIG. 4 is a schematic diagram of the configuration of an example of the second prior art apparatus.
Referring to FIG. 3, the first prior art apparatus includes is associated with a motor 31 which is operated to adjust a motor-controlled mechanism, such as a power mirror assembly or a power seat assembly of a motor vehicle, into a predetermined position. The apparatus includes a potentiometer 32 having a rotor mechanically linked to the rotating shaft of the motor 31. A moving contact connected to the rotor is electrically connected to an input terminal of an analog-digital converter 34. An output terminal of the analog-digital converter 34 is connected to an input terminal of a control signal generation section 35, and an output terminal of the control signal generation section 35 is connected to an input terminal of a motor rotation control section 36. An output terminal of the motor rotation control section 36 is connected to the terminals of the motor 31. A power source 38 applies a power supply voltage Vcc across the resistor of the potentiometer 32. The output (divided) voltage of the potentiometer 32 is typically being between 0 volts and Vcc, and is determined by the rotational position of the rotor (movable contact) relative to the resistor of the potentiometer 32. Because the rotor is mechanically linked to the motor shaft, the divided voltage indicates the angle of rotation of the motor 31. That is, the divided voltage received by the analog-digital converter 34 is proportional to the angle of rotation (rotational position) of the motor 31, thereby making it possible to determine the angle of rotation (position) of the motor 31 from the divided voltage. In the above-described arrangement, the motor 31 and the potentiometer 32 (located in the block indicated by the dot-dash line in FIG. 3) are integrally combined to form a unit in the vicinity of the motor 31. The control signal generation section 35 and the motor rotation control section 36 are integrally combined to form a micro control unit (MCU).
Referring to FIG. 4, the second prior art positioning apparatus is associated with a motor 31 operated to adjust a motor-controlled mechanism, such as a power mirror assembly or a power seat assembly of a motor vehicle, into a predetermined position. The second prior art apparatus includes a rotary encoder 33 having a rotor mechanically linked to the rotating shaft of the motor 31, and the rotary encoder 33 includes a detector which is electrically connected to an input terminal of a control signal generation section 35. A storage section 37 is connected to the control signal generation section 35. An output terminal of the control signal generation section 35 is connected to an input terminal of a motor rotation control section 36. An output terminal of the motor rotation control section 36 is connected to the motor 31. A power source 38 is connected between two terminals of the rotary encoder 33. In this case, since the rotor of the rotary encoder 33 is connected to the rotating shaft of the motor 31, the number of output pulses generated by the rotary encoder 33 is proportional to the rotational speed and the angle of rotation of the motor shaft of the motor 31, and the period of the output pulses is also proportional to the rotational speed and the angle of rotation of the motor shaft. That is, the number and the period of output pulses generated by the detector of the rotary encoder 33 represent the rotational speed and the rotating direction of the motor 31, and it is therefore possible to determine the rotational position of the motor 31 from these pulses. In the above-described arrangement, the motor 31 and the rotary encoder 33 (in the block indicated by the dot-dash line in FIG. 4) are integrally combined to form a unit in the vicinity of the motor 31. The control signal generation section 35, the motor rotation control section 36 and the storage section 37 are integrally combined to form a micro control unit (MCU).
Use of the above-mentioned first and second prior art apparatus will now be described.
In the first prior art apparatus, when a driver of the motor vehicle operates an appropriate operating button or operating lever to adjust the motor-controlled mechanism (e.g. a power mirror, a power seat or the like), a drive command is sent from the control signal generation section 35 to the motor rotation control section 36. In response to this drive command, the motor rotation control section 36 supplies a driving current to the motor 31, thereby causing the motor to rotate. When the motor 31 rotates in response to the driving current, the rotor of the potentiometer 32, which is linked to the rotating shaft of the motor 31, also rotates, and the divided voltage corresponding to the angle of rotation of the motor 31 is obtained through the rotor. Next, this divided voltage is converted into a digital signal by the analog-digital converter 34, and the converted digital signal is supplied to the control signal generation section 35. The control signal generation section 35 compares the digital signal with stored position information and generates a control signal corresponding to a difference between the digital signal and the stored information, and then transmits the control signal to the motor rotation control section 36. The motor rotation control section 36 continuously drives the motor 31 in accordance with the control signal, and maintains the driving operation until the angle of rotation (position) of the motor 31 becomes equal to a predetermined angle (position), thus moving the moving mechanism (for example, a mirror of a power mirror assembly or a seat of a power seat assembly) to a predetermined position.
In the second prior art position detector, when a driver of the motor vehicle operates an appropriate operating button or operating lever to adjust the motor-controlled mechanism, a drive command is sent from the control signal generation section 35 to the motor rotation control section 36. In response to this drive command, the motor rotation control section 36 supplies a driving current to the motor 31, thereby causing the motor 31 to rotate. When the motor 31 rotates in response to the supplied driving current, the rotor of the rotary encoder 33 linked to the rotating shaft of the motor 31 also rotates, and a pulse signal corresponding to the rotational speed and the rotational position of the motor 31, i.e., a pulse signal (position information) having a number of pulses and a pulse period representing the rotational speed and the rotational distance of the motor 31, is generated by the rotary encoder 33. Then this pulse signal (position information) is supplied to the control signal generation section 35 for comparison with previously-received position information and predetermined position information stored in the storage section 37. The control signal generation circuit 35 generates a control signal corresponding to the result of this comparison and supplies this signal to the motor rotation control section 36. The motor rotation control section 36 continuously drives the motor 31 at a rotational speed determined in accordance with the control signal, and controls the driving operation until the angle of rotation (position) of the motor 31 becomes equal to a predetermined angle (position), thus moving the movable mechanism, for example, a mirror of a power mirror assembly, a seat of a power seat assembly or the like, to a predetermined position.
The first prior art position detector has an advantage over the second prior art apparatus in that the divided voltage obtained from the potentiometer 32 represents an absolute position of the motor 31. However, the first prior art apparatus requires a high-priced analog-digital converter 34 for converting the divided voltage into a digital signal because the voltage value, in order to be processed by the MCU, which must be converted into a digital form.
On the other hand, the second prior art position detector has an advantage over the first prior art apparatus in that the MCU of the second prior art apparatus is capable of directly processing the pulse signal generated by the rotary encoder 33 in a digital processing manner. However, the second prior art apparatus requires the use of storage section 37 for storing the absolute position of the motor 31, and must recalculate the absolute position each time the motor 31 is driven to rotate. This is required because the pulse signal generated by the rotary encoder 33 only designates a relative rotational position of the motor 31. The absolute position must be calculated by determining the angular displacement from the previously-calculated absolute position stored in the storage section 37, which is determined by the number of pulses obtained from the rotary encoder 33. Therefore, the second prior art apparatus requires an expensive device acting as the storage section 37. Also, it is necessary to a special MCU and processing software to process the pulse signal and the memory content of the storage section 37 to calculate the absolute rotational position of the motor 31.